In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

• electro-magnetic radiation such as radio waves, visible light, x-rays, and gamma radiation (γ)
• particle radiation such as alpha radiation (α), beta radiation (β), and neutron radiation (particles of non-zero rest energy)
• acoustic radiation such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium)